Chromosome rearrangement between the Indian muntjac and Chinese muntjac is accompanied by a deletion of middle repetitive DNA

Abstract

The organizations of the genomes of two related species of Asian deer, the Indian (2n =6♂, 7♀) and Chinese muntjac (2n = 46), were compared at the cytogenetic and molecular levels. These dramatically different karyotypes preserve little apparent G-banding homology. The difference in chromosome number is coincident with a 22% reduction in haploid DNA content from 2.7 to 2.1 pg in the Chinese and Indian muntjac, respectively. The kinetics of reassociation of the Indian muntjac (equivalent C0t = 4285 M−1∙s−1) and Chinese muntjac DNA (equivalent C0t = 4362 M−1∙s−1) in 2.4 M tetraethylammonium chloride suggests conservation in amount of "single-copy" DNA. Two middle repetitive DNA sequence classes differ in both amount and in degree of repetition between the two species. A middle repetitive frequency component (935-fold repeated) represents 13% of the Indian muntjac DNA. A similar component (644-fold repeated) represents 17% of the Chinese muntjac DNA. Low repetition DNA sequence components (repeated 5- and 50-fold) represent 30 and 40% of the Indian and Chinese muntjac DNAs, respectively. These differences quantitatively account for the 0.6 pg haploid DNA content variation between species. The deletion of middle repetitive DNA has not substantively altered the distribution of restriction endonuclease DNA base composition classes as defined by buoyant density in cesium chloride. These results represent the first time that middle repetitive DNA has been directly implicated in a chromosome rearrangement within the vertebrates.